Abstract
One contributing factor to the lack of wide spread usage of software for collaborative development of diagrams is the high degree of variability in the requirements for such software. The requirements are categorized here in terms of diagram characteristics and diagram creation strategies. Various measures are proposed to characterize a potential collaborative diagramming need and to compare it to potential software systems. The categories and measures are also appropriate for evaluating the match between existing software and specific requirements. They can serve to guide future collaborative diagram software development.